HUDSON COUNTY – U.S. Sen. Robert Menendez’s relationship with a wealthy friend and frequent campaign contributor is being investigated by a federal grand jury in Miami, reported the Washington Post Friday morning.

The jury is said to be investigating Menendez’s role in advocating for the business interests of ophthalmologist Dr. Salomon Melgen. Documents that were exposed as part of an investigation showed that Menendez worked to convince the Dominican government to honor a lucrative contract with a port security company Melgen owned.

The senator also recently acknowledged that he acted on behalf of Melgen when federal healthcare officials accused Melgen of overbilling the government for care provided by a clinic he owns.

While a grand jury investigation does involve a prosecutor, it is not usually considered a formal investigation and is not guaranteed to lead to an indictment or prosecution. According to the Post, neither the FBI nor the U.S. Attorney’s office acknowledged the investigation.

The Post reported that the inquiry into Menendez was incited by the Medicare allegations against Melgen, and by claims on conservative website The Daily Caller that Menendez patronized prostitutes at a home in the Dominican Republic owned by Melgen. Thus far FBI agents have found no proof of the prostitute claims, according to sources cited by The Post, and last week a Dominican escort said in sworn court statements that she was paid to fabricate the claims that she had sex with the senator for money.

Menendez has called the prostitute allegations part of a Republican smear campaign.

Menendez declined to comment on whether he had any knowledge of the grand jury investigation, but said that he believed an investigation would show no wrongdoing.

"I welcome any review, because I believe, at the end of the day, that my actions have been appropriate," Menendez told the Post. "And just as everything that gave rise to this was a smear campaign based on slanders that drove the original story, I believe that when any review reviews the facts, they will determine that I have acted appropriately at all times."

Melgen’s attorney spoke on behalf of the doctor and delivered a similar message.

“Doctor Melgen has been a friend and supporter of Senator Menendez for over 20 years,” said the lawyer, Kirk Ogrosky. “We are confident that any inquiry will determine that Doctor Melgen acted appropriately at all times.” – Dean DeChiaro